1. Technical Field of the Invention
The present invention relates to photoprotective compositions comprising at least one aqueous phase, at least one oily phase, at least one water-soluble or water-dispersible, partially or completely neutralized, crosslinked or non-crosslinked acrylamido-2-methylpropanesulfonic acid polymer and at least one UV radiation-screening system, which screening system comprises at least one UV-A-screening agent of the 4,4-diarylbutadiene type.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation having wavelengths of between 280 nm and 400 nm allows tanning of the human epidermis, and that rays having wavelengths of between 280 nm and 320 nm, known by the name UV-B, cause erythemas and skin burns which can hamper the development of the natural tan; this UV-B radiation must therefore be screened out.
It is also known that UV-A rays having wavelengths of between 320 nm and 400 nm, which cause tanning of the skin, are capable of inducing its impairment, in particular in the case of a sensitive skin or a skin continually exposed to solar radiation. UV-A rays cause in particular a loss of elasticity of the skin and the appearance of wrinkles which lead to premature aging. They promote the onset of the erythematous reaction or amplify this reaction in some subjects and may even be responsible for phototoxic or photoallergic reactions. It is therefore desirable to also screen out UV-A radiation.
UV-A and UV-B rays must therefore be screened out and protective cosmetic compositions for the human epidermis containing UV-A and UV-B screening agents currently exist.
These anti-sun compositions are often provided in the form of an emulsion of the oil-in-water type (that is to say a cosmetically and/or dermatologically acceptable carrier consisting of an aqueous dispersive continuous phase and a fatty dispersed discontinuous phase) or of the water-in-oil type (aqueous phase dispersed in a continuous fatty phase), which contains, in various concentrations, one or more conventional fat-soluble organic screening agents and/or conventional water soluble organic screening agents capable of selectively absorbing harmful UV radiation, these screening agents (and their quantities) being selected according to the desired sun protection factor, the sun protection factor (SPF) being mathematically expressed by the ratio of the dose of UV radiation necessary to reach the erythematogenic threshold with the UV-screening agent to the dose of UV radiation necessary to reach the erythematogenic threshold without UV-screening agent. In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase.
Acrylamido-2-methylpropanesulfonic acid (AMPS) polymers are particularly suited for their cosmetic properties and their flexibility in terms of formulation, compared with the polymeric derivatives of the carboxylic acid (Carbopols supplied by Noveon). They may indeed be formulated at pH values of between 4 and 6 without their gelling properties being reduced. Among these derivatives, two large families may be mentioned:
(a) the hydrophilic or water-dispersible polymers such as neutralized and crosslinked polyacrylamido-2-methylpropanesulfonic acid supplied by Clariant under the name Hostacerin AMPS, or the copolymers of AMPS and other hydrophilic monomer(s) such as Sepigel 305 supplied by SEPPIC and Aristoflex AVC supplied by Clariant;
(b) the amphiphilic polymers comprising AMPS and alkyl recurring units such as those described in EP-1,069,142.
These acrylamido-2-methylpropanesulfonic acid polymers are particularly suitable in the manufacture of emulsions. They make it possible to obtain stable formulations within a broad range of texture and consistency ranging from milks to thickened creams.
Among the organic UV-A-screening agents available, a family of compounds which are particularly effective in the UV-A region is 1,4-benzene[di(3-methylidene-10-camphorsulfonic)]acid and its various salts, described in particular in FR-A-2,528,420 and FR-A-2,639,347; they are indeed capable of absorbing ultraviolet rays having wavelengths of between 280 nm and 400 nm, with absorption maxima of between 320 nm and 400 nm, in particular in the region of 345 nm.
However, the introduction of this type of UV-A-screening agent into photoprotective emulsions stabilized and/or thickened with an acrylamido-2-methylpropanesulfonic acid polymer can lead to a significant reduction in their viscosity or to their destabilization.
It thus appears necessary to have emulsions based on acrylamido-2-methylpropanesulfonic acid polymers which are stable and which may contain organic screening agents which are active in UV-A with comparable efficacy to that of 1,4-benzene[di(3-methylidene-10-camphorsulfonic)] acid and its different salts without the disadvantages listed above.
The expression “stable” is understood to mean that the macroscopic and microscopic appearance of the composition is not modified after 1 month at room temperature.